1. Field of the Invention
This invention relates to a method of sulfuration treatment for an InAlAs/InGaAs metamorphic high electron mobility transistor (MHEMT) and particularly to the method of making the InAlAs/InGaAs MHEMT provided lower gate leakage current, higher drain current density and wider input power swing range.
2. Description of Related Art
It is being widely known that InAlAs/InGaAs Metamorphic High Electron Mobility Transistor (MHEMT) on GaAs substrates, since an indium phosphide (InP) substrate may be replaced with the GaAs substrate, of which the cost is lower and the size may be at most 6 inches, is not fragile.
Moreover, in the InAlAs/InGaAs MHEMT, an InxAl1−xAs buffer layer lies between the GaAs substrate and a channel layer. If the InxAl1−xAs buffer layer is required to bear the stress caused by the no match of a lattice constant of the InxAl1−xAs buffer layer, the stress must not influence the channel layer as possible as it can. The InxAl1−xAs buffer layer may more flexibly adjust the content of indium (In), thereby the best channel layer being achieved.
However, the gate leakage current of the InAlAs/InGaAs MHEMT is higher than that of conventional GaAs pseudomorphic HEMT due to their high indium(In) mole fraction in the channel and Schottky layers of the InAlAs/InGaAs MHEMT. As shown in FIG. 1 illustrating an In0.5Al0.5As/In0.5Ga0.5As hetero-interface of a differential energy gap ΔE is 0.52 eV, so high Al mole fraction of an undoped In0.5Al0.5As schottky layer generate more surface states; the surface states influenced the donor injection efficiency from an upper δ-doped layer into two dimensional electron gas (2-DEG) of the undoped In0.5Ga0.5As channel layer.
It is known that the gate leakage current of the InAlAs/InGaAs MHEMT is higher, so more the surface states influenced the donor injection efficiency.
Consequently, because of the technical defects of described above, the applicant keeps on carving unflaggingly through wholehearted experience and research to develop the present invention, which can effectively improve the defects described above.